The present invention relates to a wireless communication apparatus and a wireless communication method.
The wireless local area network (wireless LAN) represented by the conventional 802.11a/b/g has employed the access control system based on carrier sense multiple access/collision avoidance (CSMA/CA). By CSMA/CA, each of wireless devices measures and detects the occupancy state of a wireless channel before using it and, only when none of the other wireless devices is transmitting, transmits frames. If collision occurs, the wireless device interrupts the transmission to set back-off at random and retransmits the frames. This enables equally allocating a frequency band to the wireless devices. Further, in response to the frames received, the transmission is confirmed by giving or not giving acknowledgement (ACK) or block ACK.
On the other hand, consider short-distance communication over a communication range of up to about several tens of centimeters: in such a case, only terminals present in this communication range will be influenced, so that the aforementioned approach may preferably be replaced by such an expected approach as to be easier and more efficient in connection.
To improve access efficiency at the terminal in a case where one-to-one communication is assumed, rather than using ACK as in the case of the conventional wireless LAN, it is more effective to transmit a response from the reception device only if frame transmission failed, that is, use only negative acknowledgement (NACK) (see, for example, Japanese Patent No. 4110522). Use of NACK enables transmitting frames in sequence if the channel status is good, thereby improving access efficiencies.
However, if an acute channel change has resulted in sudden break-up of communication between one wireless device and its communication-destination wireless device so that no transmission frames may be sent to this destination, the transmission-destination wireless device does not recognize the presence of the transmission frames and so does not transmits NACK, so that the transmission-source wireless device does not receive NACK. This has caused a problem that the transmission-source wireless device may not sense a change in status and might mistakenly recognize that communication had been successful in good channel status and so continue the communication.
There has been another problem that if the channel status got worse, NACK may occur at a higher frequency, thus preventing access efficiencies from being improved. Moreover, if the occurrence frequency of NACK suddenly rose to a high value and then lowered to 0 suddenly, it has been difficult to identify the phenomenon.